1、简介
Eureka集群提供了分区功能，这种功能设计理念来源于亚马逊云AWS创造的两个基础概念region（地域）和zone（可用区）：
- region：地域就是物理意义上的不同地域，在服务部署时会选择在用户需求大的区域建设多个机房并部署服务，这样可以减少网络不稳定带来的问题
- zone：一个region下可以划分为多个zone。也就是说一个区域的多个机房服务器，按照一定规则划分为不同的可用区（比如说一个区域有三个机房，这三个机房就可以划分为三个zone）。通过划分zone，可以达到容灾的效果，如果一个zone故障，其他zone仍然可以对外提供服务。
结合上面两个概念可知，当公司存在Eureka Server分地域部署的时候，我们可以采用Eureka集群提供的分区功能。这样可以保证某一个region中的zone注册的服务优先于另一个zone中注册的服务被调用，当前者不可用时，再去选择其他zone中注册的服务发起调用，这样可以保证服务调用的延迟降低。
Region和Zone的关系图：
2、集群部署
2.1 资源清单
本次一共搭建四台Eureka Server服务，其资源清单如下所示：
application-name |
zone |
instance-hostname |
prot |
Eureka-Ynatian |
zone-yantian |
eureka18881.com |
18881 |
Eureka-Luohu |
zone-luohu |
eureka18882.com |
18882 |
Eureka-Nanshan |
zone-yantian |
eureka18883.com |
18883 |
Eureka-Baoan |
zone-baoan |
eureka18884.com |
18884 |
Eureka Server Cluster集群图（Region-深圳、zone-罗湖、zone-盐田、zone-南山、zone-宝安）：
这里搭建的Eureka Server Cluster 是单个Region，包含四个zone，如果公司的需要的Eureka Server高可用要求特别高，可以在Region的每个zone中部署多个Eureka Server服务器。需要做分区域，参照Region Shenzhen配置多个Region即可。
2.2 配置文件
Eureka-Ynatian的Eureka Server配置文件
server:
port: 18881
spring:
application:
name: Eureka-Ynatian
eureka:
instance:
hostname: eureka18881.com
client:
prefer-same-zone-eureka: true
register-with-eureka: true
region: shenzhen
availability-zones:
shenzhen: zone-yantian,zone-luohu,zone-nanshan,zone-baoan
fetch-registry: true
service-url:
zone-yantian: http://eureka18881.com:18881/eureka/
zone-luohu: http://eureka18882.com:18882/eureka/
zone-nanshan: http://eureka18883.com:18883/eureka/
zone-baoan: http://eureka18884.com:18884/eureka/
Eureka-Luohu的Eureka Server配置文件
server:
port: 18882
spring:
application:
name: Eureka-Luohu
eureka:
instance:
hostname: eureka18882.com
client:
prefer-same-zone-eureka: true
register-with-eureka: true
region: shenzhen
availability-zones:
shenzhen: zone-luohu,zone-yantian,zone-nanshan,zone-baoan
fetch-registry: true
service-url:
zone-yantian: http://eureka18881.com:18881/eureka/
zone-luohu: http://eureka18882.com:18882/eureka/
zone-nanshan: http://eureka18883.com:18883/eureka/
zone-baoan: http://eureka18884.com:18884/eureka/
Eureka-Nanshan的Eureka Server配置文件
server:
port: 18883
spring:
application:
name: Eureka-Nanshan
eureka:
instance:
hostname: eureka18883.com
client:
prefer-same-zone-eureka: true
register-with-eureka: true
region: shenzhen
availability-zones:
shenzhen: zone-nanshan,zone-luohu,zone-yantian,zone-baoan
fetch-registry: true
service-url:
zone-yantian: http://eureka18881.com:18881/eureka/
zone-luohu: http://eureka18882.com:18882/eureka/
zone-nanshan: http://eureka18883.com:18883/eureka/
zone-baoan: http://eureka18884.com:18884/eureka/
Eureka-Baoan的Eureka Server配置文件
server:
port: 18884
spring:
application:
name: Eureka-Baoan
eureka:
instance:
hostname: eureka18884.com
client:
prefer-same-zone-eureka: true
register-with-eureka: true
region: shenzhen
availability-zones:
shenzhen: zone-baoan,zone-nanshan,zone-luohu,zone-yantian
fetch-registry: true
service-url:
zone-yantian: http://eureka18881.com:18881/eureka/
zone-luohu: http://eureka18882.com:18882/eureka/
zone-nanshan: http://eureka18883.com:18883/eureka/
zone-baoan: http://eureka18884.com:18884/eureka/
2.3 启动集群
依次启动集群中四个Eureka Server服务，等待集群之间稳定后，访问Eureka Server的Dashboard，此时在四台Eureka Server中的任意一台都可以看到相同的服务注册信息Instance currently registered with Eureka，以及DS Replicaes信息（这个不相同哦，不需要复制自己……），此时说明Eureka Server Cluster已经正常启动了。
2.4 服务注册
Eureka Server分区本质上除了达到高可用之外，最主要是为了给客户端提供最优的服务，以此来达到服务的最快响应。在Eureka Server中注册两个服务Server-01和Server-02，Server-01中metadata-map zone选择zone-yantian，Server-02中metadata-map zone选择zone-louhu。（注意两个服务的服务名均为Server）
Server-01配置文件
server:
port: 19991
spring:
application:
name: Server
eureka:
instance:
prefer-ip-address: true
metadata-map:
zone: zone-yantian
client:
region: shenzhen
availability-zones:
shenzhen: zone-yantian,zone-luohu,zone-nanshan,zone-baoan
service-url:
zone-yantian: http://eureka18881.com:18881/eureka/
zone-luohu: http://eureka18882.com:18882/eureka/
zone-nanshan: http://eureka18883.com:18883/eureka/
zone-baoan: http://eureka18884.com:18884/eureka/
fetch-registry: true
register-with-eureka: true
prefer-same-zone-eureka: true
Server-01中提供一个Rest Api端点
@RestController
@RequestMapping("/zone")
public class ZoneController {
@GetMapping
public String zone() {
return "Server zone-yantian";
}
}
Server-02配置文件
server:
port: 19992
spring:
application:
name: Server
eureka:
instance:
prefer-ip-address: true
metadata-map:
zone: zone-luohu
client:
region: shenzhen
availability-zones:
shenzhen: zone-luohu,zone-yantian,zone-nanshan,zone-baoan
service-url:
zone-yantian: http://eureka18881.com:18881/eureka/
zone-luohu: http://eureka18882.com:18882/eureka/
zone-nanshan: http://eureka18883.com:18883/eureka/
zone-baoan: http://eureka18884.com:18884/eureka/
fetch-registry: true
register-with-eureka: true
prefer-same-zone-eureka: true
Server-02中提供一个Rest Api端点
@RestController
@RequestMapping("/zone")
public class ZoneController {
@GetMapping
public String zone() {
return "Server zone-luohu";
}
}
此时访问Eureka dashboard可以看到Server 有两个实例注册到了Eureka Server Cluster中。
2.4 服务消费
创建一个服务消费者Consumer-01，用于测试服务调用分发的具体情况。
Consumer-01配置文件，其中指定metadata-map.zone为zone-luohu
server:
port: 17771
spring:
application:
name: Consumer-01
eureka:
instance:
prefer-ip-address: true
metadata-map:
zone: zone-luohu
client:
region: shenzhen
availability-zones:
shenzhen: zone-luohu,zone-yantian,zone-nanshan,zone-baoan
service-url:
zone-yantian: http://eureka18881.com:18881/eureka/
zone-luohu: http://eureka18882.com:18882/eureka/
zone-nanshan: http://eureka18883.com:18883/eureka/
zone-baoan: http://eureka18884.com:18884/eureka/
fetch-registry: true
register-with-eureka: true
prefer-same-zone-eureka: true
提供一个Rest Api访问端点：
@RestController
@RequestMapping("/consumer")
public class ZoneController {
@Autowired
private RestTemplate restTemplate;
@GetMapping
public String zone() {
return restTemplate.getForObject("http://server/zone", String.class);
}
}
在浏览器访问该端点，无论怎么刷新都会输出Server zone-louhu，说明请求一直打到了Server-02
修改Consumer-01的配置文件，修改metadata-map:zone为zone-yantian
server:
port: 17771
spring:
application:
name: Consumer-01
eureka:
instance:
prefer-ip-address: true
metadata-map:
zone: zone-yantian
client:
region: shenzhen
availability-zones:
shenzhen: zone-luohu,zone-yantian,zone-nanshan,zone-baoan
service-url:
zone-yantian: http://eureka18881.com:18881/eureka/
zone-luohu: http://eureka18882.com:18882/eureka/
zone-nanshan: http://eureka18883.com:18883/eureka/
zone-baoan: http://eureka18884.com:18884/eureka/
fetch-registry: true
register-with-eureka: true
prefer-same-zone-eureka: true
重新访问浏览器，请求Consumer-01提供的端点，此时无论怎么刷新都会输出Server zone-yantian，说明请求一直打到了Server-01
2.5 配置详解
在服务注册和服务消费中有几个非常重要的配置项prefer-same-zone-eureka和eureka.instance.metadata-map.zone
prefer-same-zone-eureka
eureka:
client:
region: shenzhen
availability-zones:
shenzhen: zone-luohu,zone-yantian,zone-nanshan,zone-baoan
service-url:
zone-yantian: http://eureka18881.com:18881/eureka/
zone-luohu: http://eureka18882.com:18882/eureka/
zone-nanshan: http://eureka18883.com:18883/eureka/
zone-baoan: http://eureka18884.com:18884/eureka/
- true：获取eureka.client.availability-zones下的zone列表，选择第一个zone进行服务注册，如果第一个注册失败，依次选择其他zone进行服务注册
- false：获取eureka.client.service-url列表，选择第一个service-url地址进行服务注册，如果第一个地址注册失败，依次选择其他service-url服务地址注册
eureka.instance.metadata-map.zone
eureka:
instance:
metadata-map:
zone: zone-yantian
eureka.instance.metadata-map.zone配置项用于标识服务提供者和服务消费者属于那个zone，服务消费者通过ribbon在Eureka Server中拉去服务列表。如果一个zone中有多个服务，则轮询每个zone中的服务列表；如果zone中的服务均不能访问，则尝试访问其他zone下的服务。
